(1) Field of the Invention
The present invention relates to dynamic transducer devices and, in particular, to a dynamic speaker device which is a small type but can reproduce a vibration of a frequency lower than about 250 Hz, more particularly about 100 Hz or less, as well as a higher frequency band.
(2) Description of the Prior Art
A known dynamic speaker comprises a magnetic assembly having a permanent magnet and a magnetic yoke with a magnetic gap. A voice coil is disposed in the magnetic gap. A vibrating plate of, usually, a cone shape is mechanically connected to the voice coil. The vibrating plate is elastically supported by spring means. When an audio signal is fed to the voice coil, the coil axially reciprocates according to the amplitude and frequency of the audio signal. Accordingly, the vibrating plate vibrates and reproduces the sound.
Generally speaking, a speaker having a vibrating plate of a small diameter cannot reproduce a low frequency sound or vibration because the vibrating amplitude is limited at the lower frequency.
In a known audio system, plural speakers of small and large diameter are often used together to cover the frequency range.
In another system which reproduces from an electric audio signal not only sound felt by ear but also vibration of, preferably, undertones lower than about 150 Hz to be directly transmitted to a body, an electromechanical vibrator is used for reproducing the mechnical vibration in addition to sound speakers, as disclosed in U.S. Pat. No. 4,064,376.
The use of two speakers of different sizes or the vibrator in addition to the speaker results in an increased size of an apparatus, device, or instrument to which they are assembled.